Usually, as an instrument that measures the particle size distribution of particles dispersed in a solvent, as disclosed in Patent Literature 1, there is a sample measuring instrument that measures a particle size distribution using a dynamic light scattering method.
This particle size distribution measuring instrument includes: a light source adapted to irradiate particles, which are dispersed in a solvent and exhibit Brownian motion, with laser light; a light detector adapted to detect interference light of lights scattered by the particles; and a calculation part adapted to obtain an autocorrelation function from a detection signal of the light detector to measure the particle size distribution.
However, in the case of any of a state where particles mutually contact or mutually connect and liquid interposes between them and a state where the shape of particles is thin thread-like and the thread-like particles mutually tangle to form a net-like structure (these states are called gel states), due to uneven internal structure, a specific autocorrelation function is obtained depending on an irradiation site irradiated with the laser light, and as a result, a sample cannot be accurately analyzed. Also, when foreign bodies different from the particles as a measurement target are contained in the solvent as well, the foreign bodies irradiated with the laser light prevents the sample from being accurately analyzed because the resulting autocorrelation function is different from a proper autocorrelation function of the measurement target particles.